The idea is to have the original custom message that was sent to be part of the thread when sending an addtl message directly to the recipient from within the workflow.
Proof Owner sends proof to recipient with a custom message. The proof deadline passes and the proof owner sends a follow up message from with the workflow to the recipient. The follow up message does not contain any of the original custom message and the proof owner ends up copying and pasting that original message into the follow up message.
This is similar to this idea if you would want to combine the ask.